The present invention relates to laser printers, and more particularly to a multilevel image printing device which can produce half-tones.
In a conventional laser printer, as shwon in FIG. 1, a constant power laser beam 1 is outputted by a laser beam source 1, an image signal outputted by an image outputting section 4 is applied to a drive circuit 3, and a modulator 2 is controlled by the output of the drive circuit 3, wherein the constant power laser beam outputted by the laser beam source 1 is modulated in accordance with the image signal. The laser beam thus modulated is applied to a recording sheet to form an image thereon using a conventional method.
In a conventional laser printer of this type, the laser beam is modulated with only two levels (white and black levels). That is, such a printer which can print only two levels of density cannot produce a multilevel image print. Furthermore, the conventional laser printer is disadvantageous in that it requires a modulator.
A laser printer for printing a multilevel image is available which prints a multilevel image by decreasing the picture element density of a recording sheet as shown in FIG. 2. In this laser printer, each of the picture elements 5a, 5b, 5c, etc. is divided into n regions (n being an integer larger than one), and half-tones are reproduced by the utilization of the number of black elements of the n regions. However, this method suffers from a drawback in that the picture element density is lowered.
An object of this invention is thus to provide a multilevel image printing device in which the difficulties accompanying the above-described two methods have been eliminated, the provision of the modulator is unnecessary, the picture element density is high, and half-tones can be reproduced.